1. Field of the Invention
The present invention relates to a power output apparatus, a vehicle equipped with the power output apparatus, a driving system, and a control method of the power output apparatus.
2. Description of the Prior Art
In a power output apparatus for a hybrid vehicle equipped with an internal combustion engine and a driving motor arranged to output a driving power and with a motor arranged to crank and start the internal combustion engine, one proposed technique computes a battery output demand based on a drive point of the internal combustion engine and a torque command of the driving motor, which are set corresponding to an output demand for a driveshaft. When the output demand exceeds a rated power of a battery, the proposed technique corrects the torque command of the driving motor to keep the output demand at or below an instantaneous output set based on the state of charge of the battery and a battery temperature (see Japanese Patent Laid-Open No. 2002-058113). The power output apparatus of this prior art technique controls the internal combustion engine and the driving motor to operate the internal combustion engine at the set drive point and operate the driving motor with the set or corrected torque command during only an allowable output time. Compared with a system of restricting the output limit of the battery to its rated power, this proposed technique ensures sufficient exertion of the battery performance and allows size reduction of the battery and the whole power output apparatus.
The battery adopted for an accumulator of the power output apparatus generally has a lower limit voltage in a specific voltage range that ensures sufficient battery performance without deterioration. Some type of the battery may start deterioration by continuous discharge at a high current level even when the output voltage has not yet reached the lower limit voltage. In the power output apparatus equipped with such a battery, there is a potential that continuous discharge of the battery at a high current level may cause a start of deterioration of the battery in the course of power output from only the driving motor with the operation of the internal combustion engine stopped. It is thus desirable to start the operation of the internal combustion engine according to the state of the battery. There is, however, a conflicting requirement for the improved fuel consumption in the power output apparatus. It is thus required to balance protection of the battery with improvement of the fuel consumption.